The present invention relates to crosslinking agents having etherified carbamate functionality, and to curable compositions containing them.
Coating compositions used in the original automotive equipment market are being called to more and more stringent performance requirements. Coating systems are expected to provide lasting weatherability, durability, resistance to acid etching, and mar resistance, while maintaining outstanding appearance properties. Coating systems used in certain applications, such as on plastic substrates, must also be flexible. Additionally, automotive coating compositions are expected to be available in environmentally friendly formulations.
Some coating compositions cured via acid-epoxy cure mechanisms, while providing excellent acid etch resistance, offer only marginal mar resistance. Conventional coating compositions cured with aminoplast crosslinking agents have been known for superior durability, but it has only been recently that aminoplast-cured coatings providing acid etch resistance have become available. Moreover, aminoplast-cured systems typically suffer from high photo-oxidation rates due to the breakdown of the aminotriazine ring inherently found in most aminoplast resins. Such degradation is due to prolonged exposure to ultraviolet light.
It would be desirable to provide crosslinking agents and curable compositions suitable for use as film-forming compositions in the automotive and industrial markets that overcome the drawbacks of the prior art, providing both appearance and performance properties now considered essential in automotive applications.
The present invention provides a reaction product of reactants comprising:
a) a polyisocyanate;
b) a hydroxyalkyl carbamate;
c) an aldehyde; and
d) at least one monohydric alcohol. The reaction product is suitable for use in a variety of curable compositions, which are also provided.
Additionally provided is a composition of matter comprising the structure: 
wherein Q is a multi-valent organic moiety containing urethane linkages; X is H, xe2x80x94CH2OH, or xe2x80x94CH2ORxe2x80x2; Rxe2x80x2 is an alkyl or aryl group having from 1 to 12 carbon atoms; and y is at least 2. The reaction product described above may have the structure (i).
Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term xe2x80x9cabout.xe2x80x9d Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.
Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical values, however, inherently contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.
Also, it should be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of xe2x80x9c1 to 10xe2x80x9d is intended to include all sub-ranges between (and including) the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10.
The reaction product of the present invention is typically prepared by reacting together:
a) a polyisocyanate;
b) a hydroxyalkyl carbamate;
c) an aldehyde; and
d) at least one monohydric alcohol.
The polyisocyanate a) may be selected from one or more polyisocyanates, such as diisocyanates and triisocyanates including biurets and isocyanurates. Biurets of any suitable diisocyanate including 1,4-tetramethylene diisocyanate and 1,6-hexamethylene diisocyanate may be used as reactant a) in the preparation of the reaction product of the present invention. Also, biurets of cycloaliphatic diisocyanates, such as isophorone diisocyanate and 4,4xe2x80x2-methylene-bis-(cyclohexyl isocyanate), can be employed. Examples of suitable aralkyl diisocyanates from which biurets may be prepared are meta-xylylene diisocyanate and xcex1,xcex1,xcex1xe2x80x2,xcex1xe2x80x2-tetramethylmeta-xylylene diisocyanate. The diisocyanates themselves may also be used as reactant a) in the preparation of the reaction product of the present invention.
Trifunctional isocyanates may also be used as reactant a), for example, trimers of isophorone diisocyanate, triisocyanato nonane, triphenylmethane triisocyanate, 1,3,5-benzene triisocyanate, 2,4,6-toluene triisocyanate, an adduct of trimethylol and tetramethyl xylene diisocyanate sold under the trade name CYTHANE 3160 by CYTEC Industries, and DESMODUR N 3300, which is the isocyanurate of hexamethylene diisocyanate, available from Bayer Corporation. Specifically used polyisocyanates are cyclic isocyanates, particularly, isocyanurates of diisocyanates such as hexamethylene diisocyanate and isophorone diisocyanate.
The polyisocyanate used as reactant a) may also be one of those disclosed above, chain extended with one or more polyamines and/or polyols using suitable materials and techniques known to those skilled in the art.
In the preparation of the reaction product of the present invention, the polyisocyanate reactant a) is used in an amount of 5 to 70 percent by weight, based on the total weight of reactants used to prepare the reaction product.
The hydroxyalkyl carbamate used as reactant b) typically contains about 3 to about 7 carbon atoms. Examples include hydroxyethyl carbamate, hydroxypropyl carbamate, hydroxybutyl carbamate, and the like. Reaction products of ammonia and hydroxyl functional carbonates, such as glycerin carbonate, are also suitable. Hydroxypropyl carbamate and hydroxyethyl carbamate are most often used. Reactant b) is used in an amount of 1 to 60 percent by weight, based on the total weight of reactants used to prepare the reaction product.
The aldehyde c) most often used in the preparation of the reaction product of the present invention is formaldehyde. Other aldehydes, such as acetaldehyde, propanaldehyde, butyraldehyde, furfural, benzaldehyde, acrolein, methacrolein, and glyoxal are also suitable. The aldehyde c) is used in an amount of 1 to 60 percent by weight, based on the total weight of reactants used to prepare the reaction product.
Alkylol groups formed during the reaction of a), b), and c) are at least partially etherified by reaction with at least one monohydric alcohol d). Any monohydric alcohol can be employed for this purpose. Particularly suitable alcohols may have up to 12 carbon atoms, most typically have from 1 to 6 carbon atoms, and include methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, pentanol, hexanol, cyclohexanol, and others, as well as benzyl alcohol and other aromatic alcohols, cyclic alcohols, such as cyclohexanol, monoethers of glycols, and halogen-substituted or other substituted alcohols, such as 3-chloropropanol and butoxyethanol. Most commonly, methanol, isobutanol, and/or n-butanol are used.
In the preparation of the reaction product of the present invention, the monohydric alcohol d) is used in an amount of 1 to 70 percent by weight, based on the total weight of reactants used to prepare the reaction product.
The urethane oligomer or polymer having carbamate functional groups may be alkylolated by reaction with an aldehyde. Examples of suitable aldehydes include those mentioned above, with formaldehyde being most often used. Alkylolation may be performed in an aqueous or alcoholic medium, using techniques known to those skilled in the art; for example, at temperatures of about 10xc2x0 C. to about 100xc2x0 C. in aqueous medium, and about 10xc2x0 C. to about 170xc2x0 C. in organic medium.
The alkylolated polymer or oligomer may then optionally be etherified by reaction with an alcohol using conventional techniques. Suitable alcohols contain about 1 to about 12 carbon atoms and include methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, pentanol, and cyclohexanol. Isobutanol, n-butanol, and methanol are most often used.
Alkylolation and etherification of the carbamate functional polymer or oligomer may be done in one step by reacting the carbamate functional polymer or oligomer with an aldehyde in an acidic, alcoholic medium such that the alcohol solvent which is in stoichiometric excess participates in the reaction. Alternatively, the alkylolation may first be carried out in a basic aqueous or alcoholic medium. After the alkylolation reaction is complete, the reaction mixture is treated with acid in order to neutralize the base and establish an acidic pH. If the reaction was run under aqueous conditions, the etherifying alcohol can be added to the reaction mixture prior to acidification. The reaction mixture is then typically heated to accomplish the etherification reaction.
In either of the scenarios outlined above, if the etherifying alcohol is immiscible with water the reaction can be heated to reflux and water can be removed via azeotropic distillation in order to drive the equilibrium in favor of the etherification reaction. Partial etherification is possible by stopping the reaction once an amount of water is removed corresponding to the desired degree of etherification. If the alcohol is miscible with water (e.g. methanol) the reaction mixture is simply heated and held until the desired degree of etherification or system equilibrium is reached. If desired, water can be stripped from the reaction mixture with the alcohol once the reaction is complete at a neutral or slightly basic pH to prevent gelling the reaction product.
In one embodiment of the invention there is provided a composition of matter comprising the structure: 
wherein Q is a multi-valent organic moiety containing urethane linkages; X is H, xe2x80x94CH2OH, or xe2x80x94CH2ORxe2x80x2; Rxe2x80x2 is an alkyl or aryl group having from 1 to 12 carbon atoms; and y is at least 2. The reaction product described above may have the structure (i). As mentioned earlier, Rxe2x80x2 is typically an alkyl or aryl group having from 1 to 12 carbon atoms, and may be linear or branched, cyclic, aralkyl, or alkaryl, and may contain heteroatom substituents. Rxe2x80x2 is most often the residue of a monohydric alcohol and contains from 1 to 6 carbon atoms.
The moiety Q typically is derived from a polyisocyanate and contains at least 2 urethane linkages. The moiety Q may contain groups of the structure xe2x80x94Nxe2x80x94CH2xe2x80x94ORxe2x80x2, formed during etherification of the urethane linkages. Q may contain cyclic moieties, particularly when derived from isocyanurates. In a specific embodiment, Q has the structure: 
wherein X and y are as described above, Rxe2x80x3 is a divalent group, and Rxe2x80x2xe2x80x3 is a residue of a polyisocyanate. Rxe2x80x3 may be linear or branched, cyclic, alkaryl or aralkyl and may contain heteroatom substituents. Rxe2x80x3 is most often an alkylene group having from 1 to 6 carbon atoms. Rxe2x80x2xe2x80x3 is most often a residue of an isocyanurate.
In a separate embodiment of the present invention, the reaction product or composition of matter described above is present as a crosslinking agent in a curable composition comprising:
a) the reaction product or composition of matter described above, typically present in an amount of 1 to 99, often 1 to 50 percent by weight based on the total weight of resin solids in the curable composition; and
b) at least one polymer having functional groups that are reactive with the reaction product or composition of matter of a), typically present in a total amount of 1 to 99, often 20 to 85 percent by weight based on the total weight of resin solids in the curable composition. The composition of this embodiment is suitable for use as a curable film-forming composition.
Useful functional polymers for use as component b) in the curable composition of the present invention include vinyl polymers, acrylic polymers, polyesters, including alkyds, polyurethanes, polyethers and copolymers, and mixtures thereof. As used herein, the term xe2x80x9cpolymerxe2x80x9d is meant to refer to oligomers and both homopolymers and copolymers. Unless stated otherwise, as used in the specification and the claims, molecular weights are number average molecular weights for polymeric materials indicated as xe2x80x9cMnxe2x80x9d and obtained by gel permeation chromatography using a polystyrene standard in an art-recognized manner.
The polymer (b) may comprise reactive functional groups selected from hydroxyl, carboxylic acid, amide, thiol, urea, carbamate, thiocarbamate, and mixtures thereof. In one embodiment of the present invention, the polyfunctional polymer (b) comprises carbamate functional groups of the structure: 
wherein Z is H, or an alkyl or aryl group containing 1 to 12 carbon atoms and may be linear or branched, cyclic, alkaryl or aralkyl and may contain heteroatom substituents.
Suitable functional polymers include acrylic polymers such as copolymers of one or more alkyl esters of acrylic acid or methacrylic acid, optionally together with one or more other polymerizable ethylenically unsaturated monomers. Useful alkyl esters of acrylic acid or methacrylic acid include aliphatic alkyl esters containing from 1 to 30, and often 4 to 18 carbon atoms in the alkyl group. Non-limiting examples include methyl methacrylate, ethyl methacrylate, butyl methacrylate, ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate. Suitable other copolymerizable ethylenically unsaturated monomers include vinyl aromatic compounds such as styrene and vinyl toluene; nitrites such as acrylonitrile and methacrylonitrile; vinyl and vinylidene halides such as vinyl chloride and vinylidene fluoride and vinyl esters such as vinyl acetate.
The acrylic polymer can include hydroxyl functional groups, which are often incorporated into the polymer by including one or more hydroxyl functional monomers in the reactants used to produce the copolymer. Useful hydroxyl functional monomers include hydroxyalkyl acrylates and methacrylates, typically having 2 to 4 carbon atoms in the hydroxyalkyl group, such as hydroxyethyl acrylate, hydroxypropyl acrylate, 4-hydroxybutyl acrylate, hydroxy functional adducts of caprolactone and hydroxyalkyl acrylates, and corresponding methacrylates. The acrylic polymer can be prepared with N-(alkoxymethyl)acrylamides and N-(alkoxymethyl) methacrylamides, which result in self-crosslinking acrylic polymers.
Hydroxyl functional groups may be incorporated into the acrylic polymer by using one or more ethylenically unsaturated beta-hydroxy ester functional monomers. Such monomers can be prepared from ethylenically unsaturated, epoxy functional monomers reacted with carboxylic acids having from about 1 to about 20 carbon atoms, often from about 13 to about 20 carbon atoms, or from ethylenically unsaturated acid functional monomers reacted with epoxy compounds containing at least 4 carbon atoms that are not polymerizable with the ethylenically unsaturated acid functional monomer.
Useful ethylenically unsaturated, epoxy functional monomers include glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether, methallyl glycidyl ether, 1:1 (molar) adducts of ethylenically unsaturated monoisocyanates such as meta-isopropenyl-alpha,alpha-dimethylbenzyl isocyanate with hydroxy functional monoepoxides such as glycidol, and glycidyl esters of polymerizable polycarboxylic acids such as maleic acid, fumaric acid, and crotonic acid. Most often used are the epoxy-functional acrylates such as glycidyl acrylate, epoxy functional methacrylates such as glycidyl methacrylate, or mixtures thereof. Glycidyl acrylate and glycidyl methacrylate are most often used.
Examples of saturated carboxylic acids include saturated monocarboxylic acids such as those which are noncrystalline at room temperature, particularly those having branched structures. Isostearic acid is most often used. As used herein, the term xe2x80x9csaturatedxe2x80x9d as in the phrase xe2x80x9csaturated monocarboxylic acidxe2x80x9d is intended to denote the absence of ethylenic unsaturation but is not intended to exclude aromatic unsaturation as found, for example, in a benzene ring.
Useful ethylenically unsaturated acid functional monomers include monocarboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid; dicarboxylic acids such as itaconic acid, maleic acid, and fumaric acid; and monoesters of dicarboxylic acids such as monobutyl maleate and monobutyl itaconate. The ethylenically unsaturated acid functional monomer and epoxy compound are typically reacted in a 1:1 equivalent ratio. The epoxy compound does not contain ethylenic unsaturation which would participate in free radical-initiated polymerization with the unsaturated acid functional monomer. Useful epoxy compounds include 1,2-pentene oxide, styrene oxide and glycidyl esters or ethers, typically containing from 8 to 30 carbon atoms, such as butyl glycidyl ether, octyl glycidyl ether, phenyl glycidyl ether, and para-(tertiary butyl) phenyl glycidyl ether. Most often-used glycidyl esters include those of the structure: 
where R is a hydrocarbon radical containing from about 4 to about 26 carbon atoms. Typically, R is a branched hydrocarbon group having from about 8 to about 10 carbon atoms, such as neopentanoate, neoheptanoate or neodecanoate. Suitable glycidyl esters of carboxylic acids include those commercially available from Shell Chemical Company under the trademark CARDURA(copyright) E; and from Exxon Chemical Company under the trademark GLYDEXX(copyright)-10.
Carbamate functional groups can be included in the acrylic polymer by copolymerizing the acrylic monomers with a carbamate functional vinyl monomer, such as a carbamate functional alkyl ester of methacrylic acid, or by reacting a hydroxyl functional acrylic polymer with a low molecular weight carbamate functional material, such as can be derived from an alcohol or glycol ether, via a transcarbamoylation reaction. In this reaction, a low molecular weight carbamate functional material derived from an alcohol or glycol ether is reacted with the hydroxyl groups of the acrylic polyol, yielding a carbamate functional acrylic polymer and the original alcohol or glycol ether.
The low molecular weight carbamate functional material derived from an alcohol or glycol ether may be prepared by reacting the alcohol or glycol ether with urea in the presence of a catalyst. Suitable alcohols include lower molecular weight aliphatic, cycloaliphatic, and aromatic alcohols such as methanol, ethanol, propanol, butanol, cyclohexanol, 2-ethylhexanol, and 3-methylbutanol. Suitable glycol ethers include ethylene glycol methyl ether and propylene glycol methyl ether. Propylene glycol methyl ether and methanol are most often used. Other useful carbamate functional monomers are disclosed in U.S. Pat. No. 5,098,947, which is incorporated herein by reference.
Amide functionality may be introduced to the acrylic polymer by using suitably functional monomers in the preparation of the polymer, or by converting other functional groups to amido-groups using techniques known to those skilled in the art. Likewise, other functional groups may be incorporated as desired using suitably functional monomers if available or conversion reactions as necessary.
The acrylic polymer can be prepared by solution polymerization techniques. In conducting the reaction, the monomers are heated, typically in the presence of a free radical initiator such as organic peroxides or azo compounds, for example, benzoyl peroxide or N,N-azobis(isobutyronitrile) and optionally a chain transfer agent, in an organic solvent in which the ingredients as well as the resultant polymer product are compatible. Typically, the organic solvent is charged to a reaction vessel and heated to reflux, optionally under an inert atmosphere. The monomers and other free radical initiator are added slowly to the refluxing reaction mixture. After the addition is complete, some additional initiator may be added and the reaction mixture held at an elevated temperature to complete the reaction.
The acrylic polymer typically has a number average molecular weight of from about 900 to 13,000, often from about 1000 to 5000 as determined by gel permeation chromatography using a polystyrene standard. The acrylic polymers have functional group equivalent weights less than about 5000, often within the range of about 140 to 2500, based on equivalents of reactive functional groups. The term xe2x80x9cequivalent weightxe2x80x9d is a calculated value based on the relative amounts of the various ingredients used in making the specified material and is based on the solids of the specified material. The relative amounts are those that result in the theoretical weight in grams of the material, such as a polymer produced from the ingredients, and yield a theoretical number of the particular functional group that is present in the resulting polymer. The theoretical polymer weight is divided by the theoretical number to give the equivalent weight. For example, hydroxyl equivalent weight is based on the equivalents of reactive pendant and/or terminal hydroxyl groups in a hydroxyl-containing polymer.
As discussed above, the functional polymer used in the curable film-forming composition of the present invention may alternatively be an alkyd resin or a polyester. Such polymers can be prepared in a known manner by condensation of polyhydric alcohols and polycarboxylic acids. Suitable polyhydric alcohols include ethylene glycol, propylene glycol, butylene glycol, 1,6-hexylene glycol, neopentyl glycol, diethylene glycol, glycerol, trimethylol propane, 2,2,4-trimethyl-1,3-pentanediol, 2,2-dimethyl-3-hydroxypropyl-2,2-dimethyl-3-hydroxypropionate, pentaerythritol, and the like. Suitable polycarboxylic acids include succinic acid, adipic acid, azelaic acid, sebacic acid, maleic acid, fumaric acid, phthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, methylhexahydrophthalic acid, and trimellitic acid. Besides the polycarboxylic acids mentioned above, functional equivalents of the acids such as anhydrides where they exist or lower alkyl esters of the acids such as methyl esters can be used. Polyesters prepared from polycarboxylic acids and epoxides or polyepoxides as known to those skilled in the art may also be used. Where it is desired to produce air-drying alkyd resins, suitable drying oil fatty acids can be used and include those derived from linseed oil, soya bean oil, tall oil, dehydrated castor oil, or tung oil. The polyesters and alkyd resins can contain a portion of free hydroxyl and/or carboxyl groups that are available for further crosslinking reactions by adjusting the stoichiometry of the reactants used to prepare the polyester or alkyd.
Carbamate functional groups may be incorporated into the polyester by first forming a hydroxyalkyl carbamate which can be reacted with the polyacids and polyols used in forming the polyester. The hydroxyalkyl carbamate is condensed with acid functionality on the polyester, yielding terminal carbamate functionality. Carbamate functional groups may also be incorporated into the polyester by reacting terminal hydroxyl groups on the polyester with a low molecular weight carbamate functional material via a transcarbamoylation process similar to the one described above in connection with the incorporation of carbamate groups into the acrylic polymers, or by reacting isocyanic acid with a hydroxyl functional polyester.
Other functional groups, such as amide, thiol, urea, and thiocarbamate, may be incorporated into the polyester or alkyd resin as desired using suitably functional reactants if available, or conversion reactions as necessary to yield the desired functional groups. Such techniques are known to those skilled in the art.
A particularly suitable polyester may be prepared from trimethylol propane, neopentyl glycol, 2,2,4-trimethyl-1,3-pentanediol, and hexahydrophthalic anhydride, transcarbamoylated with methyl carbamate. The preparation of this polyester is described in the examples that follow.
The polyester polymer typically has a number average molecular weight of from about 600 to 3000, often from about 800 to 1500 as determined by gel permeation chromatography using a polystyrene standard, and a functional group equivalent weight within the range of about 200 to 1500, often about 300 to 400, based on equivalents of reactive pendant or terminal functional groups.
Polyurethanes can also be used as the functional polymer in the curable film-forming composition. Useful polyurethanes include polymeric polyols which are prepared by reacting polyhydric alcohols, polyester polyols or acrylic polyols, such as those mentioned above or polyether polyols, such as those mentioned below with a polyisocyanate such that the OH/NCO equivalent ratio is greater than 1:1 so that free hydroxyl groups are present in the product. Alternatively, isocyanate functional polyurethanes may be prepared using similar reactants in relative amounts such that the OH/NCO equivalent ratio is less than 1:1, and the isocyanate functional polyurethanes may be modified to contain functional groups that are reactive with the reaction product or composition of matter of a).
The organic polyisocyanate that is used to prepare the polyurethane polymer can be an aliphatic or aromatic polyisocyanate or mixtures thereof. Diisocyanates are most often used, although higher polyisocyanates can be used in place of or in combination with diisocyanates. Examples of suitable aromatic diisocyanates include 4,4xe2x80x2-diphenylmethane diisocyanate and toluene diisocyanate. Examples of suitable aliphatic diisocyanates include straight chain aliphatic diisocyanates such as 1,6-hexamethylene diisocyanate. Also, cycloaliphatic diisocyanates such as isophorone diisocyanate and 4,4xe2x80x2-methylene-bis-(cyclohexyl isocyanate) can be used. Examples of suitable higher polyisocyanates include 1,2,4-benzene triisocyanate and polymethylene polyphenyl isocyanate. Additional polyisocyanates such as those disclosed above in the preparation of the reaction product of the present invention may also be used.
Terminal and/or pendent carbamate functional groups can be incorporated into the polyurethane by reacting a polyisocyanate with a polymeric polyol containing the terminal/pendent carbamate groups. Alternatively, carbamate functional groups can be incorporated into the polyurethane by reacting a polyisocyanate with a polyol and a hydroxyalkyl carbamate or isocyanic acid as separate reactants. Carbamate functional groups can also be incorporated into the polyurethane by reacting a hydroxyl functional polyurethane with a low molecular weight carbamate functional material via a transcarbamoylation process similar to the one described above in connection with the incorporation of carbamate groups into the acrylic polymer. Additionally, an isocyanate functional polyurethane can be reacted with a hydroxyalkyl carbamate to yield a carbamate functional polyurethane.
Other functional groups such as amide, thiol, urea, and thiocarbamate may be incorporated into the polyurethane as desired using suitably functional reactants if available, or conversion reactions as necessary to yield the desired functional groups. Such techniques are known to those skilled in the art.
The polyurethane typically has a number average molecular weight of from about 600 to 3000, often from about 800 to 1500 as determined by gel permeation chromatography using a polystyrene standard. The polyurethanes typically have functional group equivalent weights within the range of about 200 to 1500, based on equivalents of reactive functional groups.
Examples of polyether polymers used in the curable composition of the present invention are polyalkylene ether polyols including those having the following structural formula: 
where the substituent R1 is hydrogen or lower alkyl containing from 1 to 5 carbon atoms including mixed substituents, and n is typically from 2 to 6 and m is from 8 to 100 or higher. Included are poly(oxytetramethylene) glycols, poly(oxytetraethylene) glycols, poly(oxy-1,2-propylene) glycols, and poly(oxy-1,2-butylene) glycols.
Also useful are polyether polyols formed from oxyalkylation of various polyols, for example, diols such as ethylene glycol, 1,6-hexanediol, Bisphenol A and the like, or other higher polyols such as trimethylolpropane, pentaerythritol, and the like. Polyols of higher functionality that can be utilized as indicated can be made, for instance, by oxyalkylation of compounds such as sucrose or sorbitol. One commonly utilized oxyalkylation method is reaction of a polyol with an alkylene oxide, for example, propylene or ethylene oxide, in the presence of an acidic or basic catalyst. Polyethers used most often include those sold under the names TERATHANE and TERACOL, available from E. I. du Pont de Nemours and Company, Inc., and POLYMEG, available from Q O Chemicals, Inc., a subsidiary of Great Lakes Chemical Corp.
Most often, pendant or terminal carbamate functional groups may be incorporated into the polyethers by a transcarbamoylation reaction as described above.
Other functional groups such as amide, thiol, urea, and thiocarbamate may be incorporated into the polyether as desired using suitably functional reactants if available, or conversion reactions as necessary to yield the desired functional groups. The polyether polymer typically has a number average molecular weight of from about 500 to 5000, more typically from about 900 to 3200 as determined by gel permeation chromatography using a polystyrene standard, and an equivalent weight of within the range of 140 to 2500, often about 500, based on equivalents of reactive pendant or terminal functional groups.
The curable composition may further include one or more auxiliary crosslinking agents such as free and/or capped polyisocyanates; triazine compounds of the formula: C3N3(NHCOXR)3, wherein X is nitrogen, oxygen, sulfur, phosphorus, or carbon, and R is a lower alkyl group having one to twelve carbon atoms, or mixtures of lower alkyl groups, and conventional aminoplast crosslinking agents.
Suitable polyisocyanates include any of those disclosed above. Any suitable aliphatic, cycloaliphatic, or aromatic alkyl monoalcohol or phenolic compound may be used as a capping agent for the polyisocyanate. Examples include lower aliphatic alcohols such as methanol, ethanol, and n-butanol; cycloaliphatic alcohols such as cyclohexanol; aromatic-alkyl alcohols such as phenyl carbinol and methylphenyl carbinol; and phenolic compounds such as phenol itself and substituted phenols wherein the substituents do not affect coating operations, such as cresol and nitrophenol. Glycol ethers may also be used as capping agents. Suitable glycol ethers include ethylene glycol butyl ether, diethylene glycol butyl ether, ethylene glycol methyl ether and propylene glycol methyl ether.
Other suitable capping agents include pyrazoles such as 3,5-dimethyl pyrazole, oximes such as methyl ethyl ketoxime, acetone oxime and cyclohexanone oxime, lactams such as epsilon-caprolactam, and secondary amines such as dibutyl amine.
Triazine compounds of the type mentioned are described in U.S. Pat. No. 4,939,213.
Conventional aminoplast crosslinking agents are well known in the art and are described in U.S. Pat. No. 5,256,452 at column 9, lines 10-28. Useful aminoplast resins are based on the addition products of formaldehyde with an amino- or amido-group carrying substance. Condensation products obtained from the reaction of alcohols and formaldehyde with melamine, urea or benzoguanamine are most common and most often used herein. While the aldehyde employed is most often formaldehyde, other similar condensation products can be made from other aldehydes, such as acetaldehyde, crotonaldehyde, acrolein, benzaldehyde, furfural, glyoxal, and the like.
Condensation products of other amines and amides can also be used, for example, aldehyde condensates of triazines, diazines, triazoles, guanadines, guanamines, and alkyl- and aryl-substituted derivatives of such compounds, including alkyl- and aryl-substituted ureas and alkyl- and aryl-substituted melamines. Non-limiting examples of such compounds include N,Nxe2x80x2-dimethyl urea, benzourea, dicyandiamide, formaguanamine, acetoguanamine, glycoluril, ammeline, 3,5-diaminotriazole, triaminopyrimidine, and 2-mercapto-4,6-diaminopyrimidine. The aminoplast crosslinking agent may be monomeric or polymeric and may be partially or fully alkylated.
Generally, the auxiliary crosslinking agent is present in an amount ranging from about 0 to about 50 weight percent on a basis of total resin solids of the curable composition, often about 5 to about 40 weight percent.
In a separate, particular embodiment of the present invention, the reaction product or composition of matter described above may be used in a curable composition comprising:
a) the reaction product or composition of matter described above, present as a crosslinking agent in an amount of 1 to 30 percent by weight based on the total weight of resin solids in the curable composition;
b) an aminoplast crosslinking agent, present in an amount of 15 to 50 percent by weight based on the total weight of resin solids in the curable composition; and
c) an acrylic polymer having functional groups that are reactive with the crosslinking agents of a) and b), present in an amount of 20 to 84 percent by weight based on the total weight of resin solids in the curable composition.
Generally, the crosslinking agent a) is present in an amount ranging from about 1 to about 30 weight percent on a basis of total resin solids of the curable composition as noted above, often about 5 to about 15 weight percent.
The curable composition further includes an aminoplast crosslinking agent b). Useful aminoplast resins include any of those disclosed above.
Generally, the aminoplast crosslinking agent b) is present in an amount ranging from about 15 to about 50 weight percent on a basis of total resin solids of the curable composition as noted above, often about 20 to about 35 weight percent.
The acrylic polymer c) is typically present in an amount ranging from about 20 to about 84 weight percent on a basis of total resin solids of the curable composition as noted above, often about 45 to about 70 weight percent.
The acrylic polymer c) is typically a copolymer of one or more alkyl esters of acrylic acid or methacrylic acid optionally together with one or more other polymerizable ethylenically unsaturated monomers as discussed above.
The acrylic polymer often has beta-hydroxy ester functionality and, in a specific embodiment, comprises a polymer of:
1) an ethylenically unsaturated, beta-hydroxy ester functional monomer;
2) about 5 to about 50, often 10 to 30, percent by weight, based on total solid weight of monomers used to prepare the polymer, of a polymerizable ethylenically unsaturated, hydroxyalkyl functional monomer different from 1);
3) about 0 to about 40 percent by weight based on the total solid weight of monomers used to prepare the monomer of a vinyl aromatic monomer;
4) about 0 to about 60, often 0 to 30, percent by weight, based on the total solid weight of monomers used to prepare the polymer, of at least one alkyl ester of acrylic acid or methacrylic acid; and
5) about 0 to about 20 percent by weight, based on the total solid weight of monomers used to prepare the polymer, of at least one ethylenically unsaturated monomer different from 1), 2), 3), and 4) above.
The beta-hydroxy ester functional monomer can be prepared from ethylenically unsaturated, epoxy functional monomers reacted with carboxylic acids having from about 1 to about 20 carbon atoms, or from ethylenically unsaturated acid functional monomers reacted with epoxy compounds containing at least 4 carbon atoms that are not polymerizable with the ethylenically unsaturated acid functional monomer. Such monomers are discussed above.
The beta-hydroxy ester functional monomer is typically present in the polymer in an amount of 1 to about 70 percent, often about 10 to about 70, more often about 20 to about 55 percent by weight, based on the total solid weight of monomers used to prepare the polymer.
Hydroxyethyl methacrylate is the most often used hydroxyalkyl monomer 2), and is typically present in an amount of about 10 to about 30 percent by weight, based on the total solid weight of monomers used to prepare the polymer. Suitable vinyl aromatic monomers and acrylic or methacrylic acid esters include those disclosed above.
In addition to hydroxyl groups, the polymer may have carbamate functional groups. Such groups may be incorporated into the polymer as discussed above.
The acrylic polymer used in the curable composition typically has a weight average molecular weight of about 2,000 to about 25,000, often 3,000 to 10,000 as determined by gel permeation chromatography using a polystyrene standard. The hydroxyl equivalent weight of the polymer is generally about 200 to about 800, often about 300 to about 500.
In each embodiment of the present invention, the curable compositions may optionally contain a mixture of other polymers separate from and in addition to the functional group-containing polymer(s) that are reactive with the crosslinking agent(s). The additional polymer(s) may or may not contain functional groups and may be selected from acrylic polymers, polyester polymers, which are most often used, polyurethane polymers, polyether polymers, polysiloxane polymers, polyolefins, and mixtures thereof. These polymers are often hydroxyl or carbamate functional and may be prepared as discussed above. Other functional groups include epoxide, silane, carboxylic acid, anhydride, and the like.
When the curable compositions of the present invention contain additional functional group-containing polymers, the additional polymers are present in total amounts up to 50, often about 5 to 35, more often 5 to 20 percent by weight based on the total weight of resin solids in the curable composition.
In each embodiment of the present invention, the curable composition may further include one or more auxiliary crosslinking agents as disclosed above, such as free and/or capped polyisocyanates; triazine compounds of the formula: C3N3(NHCOXR)3, wherein X is nitrogen, oxygen, sulfur, phosphorus, or carbon, and R is a lower alkyl group having one to twelve carbon atoms, or mixtures of lower alkyl groups; and conventional aminoplast crosslinking agents.
Other optional ingredients, such as catalysts, plasticizers, anti-oxidants, thixotropic agents, hindered amine light stabilizers, UV light absorbers and stabilizers may be formulated into the curable compositions of the present invention. These ingredients may be present (on an individual basis) in amounts up to 10 percent, often from about 0.1 to 5 percent by weight based on total weight of resin solids of the curable composition. Suitable catalysts include acid functional catalysts known to those skilled in the art as useful in aminoplast-cured compositions, such as phenyl acid phosphate, para-toluenesulfonic acid, dodecylbenzene sulfonic acid, and the like.
The curable compositions of the present invention may be used as curable film-forming compositions and may contain color pigments conventionally used in surface coatings and may be used as high gloss monocoats; that is, high gloss pigmented coatings. By xe2x80x9chigh glossxe2x80x9d it is meant that the cured coating has a 20xc2x0 gloss and/or a DOI (xe2x80x9cdistinctness of imagexe2x80x9d) measurement of at least about 80 as measured by standard techniques known to those skilled in the art. Such standard techniques include ASTM D523 for gloss measurement and ASTM E430 for DOI measurement.
In specific embodiments of the present invention, suitable polymers or oligomers containing functional groups reactive with the crosslinking agent(s) may be used (either by themselves, combined with one another, or in combination with other polymers or oligomers) to provide coatings with flexibility acceptable for use over flexible plastic substrates. Nonlimiting examples of such polymers or oligomers are described in the examples below. By flexible plastic substrates is meant any of the common thermoplastic or thermoset synthetic materials, which would include but not be limited to polyethylene, polypropylene, thermoplastic polyolefin (TPO), reaction injected molded polyurethane (RIM), and thermoplastic polyurethane (TPU).
A specific application of the present invention is as a protective and decorative coating for pigmented plastic substrates, or mold-in-color (MIC) plastic. The curable compositions of the present invention may be applied as a high gloss clear monocoat directly to the pigmented plastic or applied over a clear adhesion promoter or clear primer which is on the surface of the pigmented plastic. One example of a clear adhesion promoter is MPP-4205 and is available from PPG Industries, Inc.
The curable compositions of the present invention are additionally often used as clear coats in multi-component composite coating compositions such as color-plus-clear composite coating compositions. A color-plus-clear composition typically comprises a base coat deposited from a pigmented or colored film-forming composition, and a transparent topcoat (clear coat) applied over the base coat.
The multi-component composite coating compositions can be applied to various substrates to which they adhere, including wood, metals, glass, cloth, polymeric substrates, and the like. They are particularly useful for coating metals and elastomeric substrates that are found on motor vehicles. The compositions can be applied by conventional means including brushing, dipping, flow coating, spraying, and the like, but they are most often applied by spraying. The usual spray techniques and equipment for air spraying and electrostatic spraying and either manual or automatic methods can be used.
First, a base coat composition is applied to the surface of the substrate to be coated. The base coat composition can be waterborne, solventborne or powdered, and typically includes a film-forming resin, crosslinking material (such as are discussed above), and pigment. Non-limiting examples of suitable base coat compositions include waterborne base coats for color-plus-clear composites such as are disclosed in U.S. Pat. Nos. 4,403,003; 4,147,679; and 5,071,904, each of which is incorporated by reference herein.
After application of the base coat to the substrate, there is typically a drying or flash-off period allowed prior to the application of the clear coat. The purpose of this period is to evaporate at least a portion of the solvent or water from the base coat film. The flash-off conditions may vary by time, temperature, and/or humidity, depending on the particular base coat composition, the desired appearance, and properties of the final film. Typical times are from 1 to 15 minutes at a temperature between 70xc2x0 F. and 250xc2x0 F. (21.1xc2x0 C. and 121.1xc2x0 C.) More than one base coat layer and multiple topcoat layers may be applied to the substrate to develop optimum appearance. Typically, the base coat thickness ranges from about 0.1 to about 5 mils (about 2.54 to about 127 microns), and often about 0.4 to about 1.5 mils (about 10.16 to about 38.1 microns) in thickness.
After application of the base coat, the topcoat described in detail above is applied. The topcoat coating composition can be applied to the surface of the base coat by any of the coating processes discussed above for applying the base coat coating composition to the substrate. The coated substrate is then heated to cure the coating layers. In the curing operation, solvents are driven off and the film-forming materials of the clear coat and the base coat are each crosslinked. The heating or curing operation is usually carried out at a temperature in the range of from 160xc2x0 F.-350xc2x0 F. (71xc2x0 C.-177xc2x0 C.) but, if needed, lower or higher temperatures may be used as necessary to activate crosslinking mechanisms. The thickness of the clear coat usually ranges from about 0.5 to about 5 mils (about 12.7 to about 127 microns), often about 1.0 to about 3 mils (about 25.4 to about 76.2 microns).
As used herein, the term xe2x80x9ccurexe2x80x9d as used in connection with a composition, e.g., xe2x80x9ca curable composition,xe2x80x9d shall mean that any crosslinkable components of the composition are at least partially crosslinked. In certain embodiments of the present invention, the crosslink density of the crosslinkable components, i.e., the degree of crosslinking, ranges from 5% to 100% of complete crosslinking. In other embodiments, the crosslink density ranges from 35% to 85% of full crosslinking. In other embodiments, the crosslink density ranges from 50% to 85% of full crosslinking. One skilled in the art will understand that the presence and degree of crosslinking, i.e., the crosslink density, can be determined by a variety of methods, such as dynamic mechanical thermal analysis (DMTA) using a Polymer Laboratories MK III DMTA analyzer conducted under nitrogen. This method determines the glass transition temperature and crosslink density of free films of coatings or polymers. These physical properties of a cured material are related to the structure of the crosslinked network.
According to this method, the length, width, and thickness of a sample to be analyzed are first measured, the sample is tightly mounted to the Polymer Laboratories MK III apparatus, and the dimensional measurements are entered into the apparatus. A thermal scan is run at a heating rate of 3xc2x0 C./min, a frequency of 1 Hz, a strain of 120%, and a static force of 0.01N, and sample measurements occur every two seconds. The mode of deformation, glass transition temperature, and crosslink density of the sample can be determined according to this method. Higher crosslink density values indicate a higher degree of crosslinking in the coating.
The curable compositions of the present invention, when used as film-forming compositions, demonstrate improved acid resistance and decreased photo-oxidation rates when compared to similar compositions that do not contain the reaction product or composition of matter described above, but instead are formulated with conventional aminoplast crosslinking agents. Not intending to be bound by any theory, it is believed that triazine rings present in conventional aminoplast crosslinking agents in coating compositions undergo photo-oxidation when exposed to ultraviolet radiation, leading to degradation of a cured film. Curable compositions of the present invention, containing the reaction product or composition of matter of the present invention, do not photo-oxidize as rapidly as conventional compositions.
The determination of acid resistance of a coating may be performed as follows:
Coated test panels measuring at least 4xe2x80x3xc3x978xe2x80x3 (10.16 cmxc3x9720.32 cm) are exposed in Jacksonville, Fla. from the last week of May through the last week of August of a calendar year. This is the standard location and exposure period (summer months) established by the North American automobile manufacturers. Upon exposure completion, the panels are hand washed with soap and water, and then rinsed with water. The rinse water is removed by squeegee, and then the panels are allowed to dry at room temperature. The panels are rated on a scale of 0 to 10 against a set of reference standards comparable to those used by General Motors Company. A rating of xe2x80x980xe2x80x99 is outstanding, with no visible etching or waterspotting. The severity of etch steadily increases up through the rating of xe2x80x9810xe2x80x99, which is severe etching and waterspotting. The determination of the photo-oxidation rate of a coating may be performed according to Ford Motor Company""s Exterior Paint Weathering Test Method PA-0148, DVM-5867.
The present invention will further be described by reference to the following examples. The following examples are merely illustrative of the invention and are not intended to be limiting. Unless otherwise indicated, all parts are by weight.